The present invention relates generally to the generating of ophthalmic lenses from lens blanks made of polymeric material or of glass.
In a conventional lens generating technique, a lens blank is mounted in a holder, and a rapidly rotating lens grinding tool is applied to the surface of the lens blank in a precisely determined manner in order to generate a desired surface on the lens blank.
In conventional lens grinding machines, as disclosed for example in Coburn U.S. Pat. No. 2,806,327, the lens grinding tool comprises a metallic cup-shaped object whose front rim defines a cutting edge encrusted with hard abrasive material such as diamond grit, carbide, or the like. The cutting edge is not sharp, but rather is radiused about a center of curvature. The tool contains a hollow tapered shank extending from a rear side thereof. The tapered shank is received in a correspondingly tapered front socket of a rotary drive shaft. A bolt extends through the shaft and is threadedly received in a threaded hole in the tool shank for urging the tapered surfaces tightly together. The shaft is rotatably mounted in a spindle housing for rotation about a horizontal longitudinal axis and is driven by a motor operably connected to a rear end of the shaft.
During a cutting operation, pressurized fluid is directed toward the cutting edge for cooling and flushing purposes. The fluid is directed from a nozzle ring which surrounds the cutting edge. A splash hood encases the tool and lens to confine the water spray.
It will be appreciated that the generation of the desired surface on a lens blank involves extremely close tolerances and thus requires close control of the orientation of the grinding tool with respect to the lens blank. The machine is typically manually or automatically adjustable for moving the tool to specific orientations for generating a properly configured surface on the lens. In order to maintain the required close tolerances, it is necessary that the location of the tool cutting edge relative to a reference plane on the machine be established with certainty so that accurate adjustments can be made.
One conventional manner of precisely locating the cutting edge involves the use of a wheel set gauge 72 of the type depicted in FIG. 2 herein. That gauge 72 can be detachably mounted on the machine, e.g., mounted on a vertical pivot pin 73 defining an axis about which a tool-carrying portion of the machine is pivotable to effect one of the tool adjustments. The gauge includes a pin 74 which terminates at a fixed location, i.e., in a fixed vertical reference plane 70 relative to the pivot axis which is situated to assure that when the cutting edge 44 touches the pin, the afore-mentioned center of curvature CC of the cutting edge lies in a vertical plane P containing the pivot axis. That is, the planes P and 70 are spaced by a distance r equal to the radius of curvature of the cutting edge. Horizontal adjustment of the tool for bringing the cutting edge into engagement with the pin is achieved by longitudinally moving the spindle housing 22 in which the rotary shaft 24 is mounted. The spindle housing is mounted in a suitable machine clamp which can be loosened to accommodate such movement, whereupon the clamp is retightened.
On occasion, it is necessary to replace the cutting tool. Such tool exchanges are necessary, for example, when converting the machine to cut lenses of different material (e.g., when changing from glass lens cutting to plastic lens cutting), or when the lenses are to be cut to a different size, requiring a larger or smaller tool, or when the cutting edge becomes excessively worn. Regardless of the reason, it is necessary to check the location of the cutting edge relative to the pivot axis each time that a tool exchange is made, because of dimensional variances between the replacement tool and the tool being replaced. That is, unless the replacement tool is gauged, it cannot be assured that the replacement tool will be dimensioned such that its cutting edge will lie in the reference plane when the replacement tool is installed in the driven shaft.
The location of the cutting edge is checked by means of the wheel set gauge, an operation which has heretofore been a laborious and time-consuming operation, often requiring from one to two hours to accomplish. Such time and effort result from the need to remove the splash hood and water hoses leading to the water spray nozzle, as well as the need to attach the wheel set gauge to the machine and possibly scrape embedded glass dust from around the spindle housing to enable the latter to be adjusted. It will be appreciated that the machine is inoperable and unproductive during this entire procedure. For small facilities employing only a single machine, such down times are not infrequent and are highly costly in terms of lost production, as well as the need to employ a skilled technician to perform the afore-described tasks.